High-strength and lightweight aluminum alloys are being increasingly employed as materials for use in applications wherein both strength characteristics and appearance characteristics are considered to be important, such as transport machines, sporting goods and machine components. For these applications, because durability is required, there is a desire for aluminum alloys having a proof stress of 350 MPa or more.
7000-series aluminum alloys obtained by adding Zn and Mg to aluminum are known as aluminum alloys which exhibit such high strength. 7000-series aluminum alloys exhibit high strength due to age-precipitation of Al—Mg—Zn-based precipitates. Also, among 7000-series aluminum alloys, those to which Cu has been added in addition to Zn and Mg exhibit the highest strength among the aluminum alloys.
7000-Series aluminum alloys are produced, for example, by hot extrusion, and are used in transport equipment such as aircraft and vehicles, sporting goods and machine components which are required to have high strength. In case they will be used in such applications, the required characteristics include, in addition to strength, resistance to stress corrosion cracking, impact absorption and ductility. For example, the aluminum alloy extruded material described in Patent Document 1 has been proposed as an example of an aluminum alloy that satisfies the above-mentioned characteristics.